System and method for transmission in a grant-free uplink transmission scheme

ABSTRACT

A system and method includes implementing, by a base station (BS), a reliable ultra-low latency transmission mechanism in a grant-free uplink transmission scheme having defined therein contention transmission unit (CTU) access regions and a plurality of CTUs. Implementing the reliable ultra-low latency transmission mechanism includes defining a reliable ultra-low latency CTU (RULL-CTU) access region from a portion of the CTU access regions of the grant-free transmission scheme, defining an RULL-CTU mapping scheme by mapping at least a portion of plurality of CTUs to the RULL-CTU access region to define a plurality of RULL-CTUs, defining a reliable ultra-low latency user equipment (RULL-UE) mapping scheme by defining rules for mapping a plurality of RULL-UEs to the plurality of RULL-CTUs in an initial pattern for initial transmissions in a first transmission time interval (TTI), and a regrouped pattern for redundant transmissions in a second TTI subsequent to the first TTI.

CROSS REFERENCE TO RELATED APPLICATIONS

The present disclosure is a continuation of U.S. patent application Ser.No. 16/907,876 filed Jun. 22, 2020, which is a continuation of U.S.patent application Ser. No. 15/989,810 filed May 25, 2018, which is acontinuation of U.S. patent application Ser. No. 15/656,199, filed Jul.21, 2017, which is a continuation of U.S. patent application Ser. No.14/606,665, filed Jan. 27, 2015, the entireties of which are herebyincorporated by reference.

FIELD

The present disclosure relates a system and method for reliable lowlatency transmission mechanism in a grant-free uplink transmissionscheme for wireless communication.

BACKGROUND

In a typical wireless network such as a long-term evolution (LTE)network, the selection of shared data channels for uplink isscheduling/grant based, and the scheduling and grant mechanisms arecontrolled by a base station (BS) in the network. A user equipment (UE)sends an uplink scheduling request to the BS. When the BS receives thescheduling request, the BS sends an uplink grant to the UE indicatingits uplink resource allocation. The UE then transmits data on thegranted resource.

SUMMARY

In some aspects, the present disclosure describes a method includingmapping a first user equipment (UE) for uplink transmission to firsttime-frequency regions of a frequency partition. The method alsoincludes configuring the first UE, using high-level signaling, toperform a configured first number of uplink transmissions including aninitial transmission and at least one retransmission irrespective ofwhether the initial transmission was successfully received, usingtime-frequency regions indicated by said mapping.

In any of the preceding aspects/embodiments, the configured first numberof uplink transmissions may be a configured first number of uplinkgrant-free transmissions.

In any of the preceding aspects/embodiments, the method may also includeconfiguring the first UE to perform frequency hopping between an initialtransmission and a retransmission.

In any of the preceding aspects/embodiments, the configured first numberof uplink transmissions may be determined based on a reliability mode ofthe first UE.

In any of the preceding aspects/embodiments, each first time-frequencyregion may be a contention transmission unit (CTU) access region furtherdefined by a signature and a pilot.

In some aspects, the present disclosure describes a method performed bya user equipment (UE). The method includes receiving, by high-levelsignaling, a mapping of the UE for uplink transmission to firsttime-frequency regions of a frequency partition. The method alsoincludes performing a configured first number of uplink transmissionsincluding an initial transmission and at least one retransmissionirrespective of whether the initial transmission was successfullyreceived, using time-frequency regions indicated by said mapping.

In any of the preceding aspects/embodiments, the configured first numberof uplink transmissions may be a configured first number of uplinkgrant-free transmissions.

In any of the preceding aspects/embodiments, the method may also includeperforming frequency hopping between an initial transmission and aretransmission.

In any of the preceding aspects/embodiments, the configured first numberof uplink transmissions may be determined based on a reliability mode ofthe UE.

In any of the preceding aspects/embodiments, each first time-frequencyregion may be a contention transmission unit (CTU) access region furtherdefined by a signature and a pilot.

In some aspects, the present disclosure describes a base stationincluding a processor, and a non-transitory computer-readable memorystoring thereon instructions. The instructions, when executed, cause theprocessor to: map a first user equipment (UE) for uplink transmission tofirst time-frequency regions of a frequency partition. The instructions,when executed, further cause the processor to configure the first UE,using high-level signaling, to perform a configured first number ofuplink transmissions including an initial transmission and at least oneretransmission irrespective of whether the initial transmission wassuccessfully received, using time-frequency regions indicated by saidmapping.

In any of the preceding aspects/embodiments, the configured first numberof uplink transmissions may be a configured first number of uplinkgrant-free transmissions.

In any of the preceding aspects/embodiments, the instructions may, whenexecuted, further cause the processor to configure the first UE toperform frequency hopping between an initial transmission and aretransmission.

In any of the preceding aspects/embodiments, the configured first numberof uplink transmissions may be determined based on a reliability mode ofthe first UE.

In any of the preceding aspects/embodiments, each first time-frequencyregion may be a contention transmission unit (CTU) access region furtherdefined by a signature and a pilot.

In some aspects, the present disclosure describes a user equipment (UE)including a processor, and a non-transitory computer-readable memorystoring thereon instructions. The instructions, when executed, cause theprocessor to receive, by high-level signaling, a mapping of the UE foruplink transmission to first time-frequency regions of a frequencypartition. The instructions, when executed, further cause the processorto perform a configured first number of uplink transmissions includingan initial transmission and at least one retransmission irrespective ofwhether the initial transmission was successfully received, usingtime-frequency regions indicated by said mapping.

In any of the preceding aspects/embodiments, the configured first numberof uplink transmissions may be a configured first number of uplinkgrant-free transmissions.

In any of the preceding aspects/embodiments, the instructions may, whenexecuted, further cause the processor to perform frequency hoppingbetween an initial transmission and a retransmission.

In any of the preceding aspects/embodiments, the configured first numberof uplink transmissions may be determined based on a reliability mode ofthe UE.

In any of the preceding aspects/embodiments, each first time-frequencyregion may be a contention transmission unit (CTU) access region furtherdefined by a signature and a pilot.

Other aspects and features of the present disclosure will becomeapparent to those ordinarily skilled in the art upon review of thefollowing description of specific embodiments in conjunction with theaccompanying figures.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the present disclosure will now be described, by way ofexample only, with reference to the attached Figures.

FIG. 1 is a block diagram of a network on which various embodiments maybe implemented;

FIG. 2 is a schematic diagram of an example configuration of variouscontention transmission unit (CTU) access units according to anembodiment;

FIG. 3A is a flow chart of base station (BS) activity in implementing anexample reliable ultra-low latency (RULL) transmission scheme accordingto an embodiment;

FIG. 3B is a flow chart of BS activity in implementing an example RULLtransmission scheme according to another embodiment;

FIG. 4 is a flow chart of an example reliable ultra-low latency userequipment (RULL-UE) activity in implementing an RULL transmissionmechanism according to an embodiment;

FIG. 5 is a schematic diagram of an example of mapping and regroupingRULL-UEs to reliable ultra-low latency CTUs (RULL-CTUs) in an RULLtransmission mechanism according to an embodiment;

FIG. 6 is a schematic diagram of an example of resolving collisionsutilizing the RULL transmission mechanism according to an embodiment;

FIG. 7 is a schematic diagram of an example RULL transmission mechanismutilizing selective redundancy transmission scheme according to anembodiment;

FIG. 8 is a schematic diagram of an example RULL transmission mechanismutilizing a RULL-CTU access region dedicated for initial transmissionsaccording to an embodiment; and

FIG. 9 is a block diagram of an example processing unit that may beutilized for implementing the devices and methods in accordance withvarious embodiments described herein.

DETAILED DESCRIPTION

Generally, embodiments of the present disclosure provide a method andsystem for a reliable ultra-low latency (RULL) transmission mechanism ina grant-free uplink transmission scheme. For simplicity and clarity ofillustration, reference numerals may be repeated among the figures toindicate corresponding or analogous elements. Numerous details are setforth to provide an understanding of the examples described herein. Theexamples may be practiced without these details. In other instances,well-known methods, procedures, and components are not described indetail to avoid obscuring the examples described. The description is notto be considered as limited to the scope of the examples describedherein.

Various embodiments are described herein in the context of a long-termevolution (LTE) wireless network. However, various embodiments may alsobe applied to other wireless networks including, for example, worldwideinteroperability for microwave access (WiMAX) networks, or futurewireless network, for example, future cellular network without cell IDfor cells.

Referring to FIG. 1, a schematic diagram of a network 100 is shown. Abase station (BS) 102 provides uplink and downlink communication withthe network 100 for a plurality of user equipment (UEs) 104-118 within acoverage area 120 of the BS 102. The BS 102 may be, for example, a celltower. FIG. 1 shows one BS 102 and eight UEs 104-118 for illustrativepurposes, however a network 100 may include more than one BS 102 and thecoverage area 120 of the BS 102 may include more or less than eight UEs104-118 in communication with the BS 102.

The BS 102 implements a grant-free uplink transmission scheme in whichcontention transmission unit (CTU) access regions are defined. Each CTUaccess region may include a number of CTUs. A CTU is a basic resource,predefined by the network 100, for contention transmissions. Each CTUmay be a combination of time, frequency, code-domain, and/or pilotelements. Code-domain elements may be, for example, CDMA (code divisionmultiple access) codes, LDS (low-density signature) signatures, SCMA(sparse code multiple access) codebooks, and the like. These possiblecode-domain elements are referred to generically as “signatures”hereinafter. Multiple UEs may contend for the same CTU. The size of aCTU may be preset by the network 100 and may take into account anexpected transmission size, the amount of desired padding, and/ormodulation coding scheme (MCS) levels. The grant-free uplinktransmission scheme may be defined by the BS 102, or it may be set in awireless standard (e.g., 3GPP). A detailed description of an examplegrant-free uplink transmission scheme and method may be found in U.S.patent application Ser. No. 13/790,673 filed on Mar. 8, 2013, entitled“System and Method for Uplink Grant-Free Transmission Scheme”, whichapplication is hereby incorporated herein by reference.

Sparse code multiple access (SCMA) is a non-orthogonal waveform withnear optimal spectral efficiency that utilizes the shaping gain ofmulti-dimensional constellation. The utilization of non-orthogonalwaveforms in SCMA enables the creation of a multiple-user multipleaccess scheme in which sparse codewords of multiple layers or users areoverlaid in code and power domains and carried over sharedtime-frequency resources. The system is overloaded if the number ofoverlaid layers is more than the length of multiplexed codewords.Overloading is achievable with moderate complexity of detection due tothe sparseness of SCMA codewords. In SCMA, coded bits are directlymapped to multi-dimensional sparse codewords selected fromlayer-specific SCMA codebooks. The major factors that control thecomplexity of the SCMA include the sparseness level of codewords, andthe multi-dimensional constellations with a low number of projectionpoints per dimension. Due to these benefits, SCMA is a technologysuitable for supporting massive connectivity. Furthermore, a blindmulti-user reception technique using Message Parsing Algorithm (MPA) canbe applied to detect users' activities and the information carried bythem simultaneously. With such blind detection capability, grant-freemultiple access can be supported. A detailed description of SCMA schemesmay be found in U.S. patent application Ser. No. 13/919,918 filed Jun.17, 2013, entitled System and Method for Designing and UsingMultidimensional Constellations, which application is incorporatedherein by reference. A detailed description of a MPA receiver may befound in U.S. patent applications Ser No. 14/212,583 filed Mar. 14,2014, entitled Low Complexity Receiver and Method for Low DensitySignature Modulation, which application is hereby incorporated herein byreference.

Referring to FIG. 2, a schematic diagram of an example of defining CTUresources within various CTU access regions in a grant-free uplinktransmission scheme is shown.

In the example, the available bandwidth of a BS 102 is divided intotime-frequency regions that define the CTU access regions. In theexample shown in FIG. 2, four CTU access regions 202-208 are defined.Each CTU access region 202-208 occupies a predefined number of resourceblocks (RBs) of the available bandwidth. The CTU access region 202, forexample, occupies four resource blocks RB1-RB4. In FIG. 2, CTUs aremapped identically to access regions 202-208, but varying views of thismapping are shown for illustrative purposes.

The frequency-time regions occupied by each CTU access region 202-208are further broken down to support six signatures (S1-S6) and six pilotsmapped to each signature to create thirty-six total pilots (P1-P36) perCTU access region 202-208. Each CTU is defined by a combination of time,frequency, signature, and pilot. In the example shown, each CTU accessregion 202-208 is able to support up to thirty-six UEs contending forthe thirty-six CTUs defined in each region. A pilot/signaturedecorrelator at the BS 102 is used to detect and decode individual UEsignals and transmissions.

The number of unique pilots defined in the grant-free uplinktransmission scheme, e.g. the thirty-six pilots per CTU access region202-208 in the example shown in FIG. 2, may depend on the number of UEssupported in the system. The specific numbers given in FIG. 2 areincluded for illustrative purposes only, and the specific configurationof the CTU access regions and CTUs, including the number of CTU accessregions 202-208 and the number of CTUs within each CTU access region,may vary depending on the network.

The grant-free uplink transmission scheme may assign a unique,identifying CTU index, I_(CTU), to each CTU in the CTU access regions202-208. UEs 104-118 determine which CTU to transmit on based on mappingrules for mapping each UE 104-118 to an appropriate CTU index. Themapping rules may be defined in a default mapping scheme. The defaultmapping scheme may be determined by the BS 102, in which case thedefault mapping scheme is sent to the UEs 104-118 utilizing, forexample, high-level signaling from the BS 102 when the UEs 104-118connect to the BS 102. Alternatively, the default mapping scheme may bedetermined by a standard, in which case the default mapping scheme isknown at the UEs104-118 prior to the UEs 104-118 connecting to the BS102.

Utilizing a default mapping scheme enables a UE to automaticallytransmit data on CTUs as soon as it enters a BS's 102 coverage area 120without scheduling signaling between the BS 102 and the UEs. The defaultmapping rules may be based on, for example, a UE's dedicated connectionsignature (DCS), its DCS index assigned by a BS, the total number ofCTUs, and/or other parameters such as subframe number.

The default mapping rules may map UEs uniformly over the availableresources taking into account the size of the CTU access regions 202-208over the time-frequency domain and the desire to reduce decodingcomplexity at the BS 102. The size of the CTU access regions 202-208 istaken into account so that UEs are not all mapped to the same subset ofavailable time-frequency resources.

In a grant-free uplink transmission scheme, a collision occurs whenmultiple UEs simultaneously access the same CTU. In a collision the BS102 is unable to estimate the individual channels of the UEs accessingthe same CTU and, therefore, cannot decode each UE's transmissioninformation. For example, assume two UEs (UE 104 and 106) are mapped tothe same CTU and their channels are h1 and h2. If both UEs transmitsimultaneously, the BS 102 can only estimate a channel of quality ofh1+h2 for both UEs 104 and 106 and the transmitted information will notbe decoded correctly. However, the BS 102 can implicitly determine whichUEs the transmission came from based on the default mapping rules, eventhough the BS 102 is unable to explicitly determine which UEs weretransmitting such as, for example, by resolving the headers of each ofthe transmissions.

In normal operation of an example grant-free uplink transmission scheme,a UE may be notified by the BS 102 when the transmission from the UE issuccessfully decoded through, for example, an acknowledgement (ACK). TheBS 102 only sends ACK signals when transmissions are successful.Therefore, if a UE does not receive an ACK signal within a predeterminedtime period, the UE determines that collision has occurred and mayretransmit the uplink transmission. Alternatively, the BS 102 may send anegative acknowledgement (NACK) signal to the UE when the transmissionfails. In this case the UE assumes transmission was successful unless aNACK signal is received at the UE.

When a collision does occur, relying on ACK/NACK feedback at the UEcreates a latency period between the time of the initial transmissionand the time that the transmission is subsequently decoded because theUE waits for a predefined period without receiving an ACK signal oruntil receiving a NACK signal, before determining that the transmissionwas unsuccessful and should be retransmitted. This latency period maybe, for example, 4 ms. In addition, a UE may wait an addition periodafter receiving ACK/NACK feedback before sending a retransmissionbecause of, for example, a random backoff procedure implemented withinthe grant-free uplink transmission scheme. This additional wait periodmay be, for example, 4 ms.

Further, if both UEs mapped to the same CTU attempt to resolve acollision by retransmitting the signal, it is possible that theretransmissions from the UEs may again collide.

In some applications it may be undesirable to wait until the UEdetermines that the initial transmission was unsuccessful beforeresending. For example, in 5G networks for teleprotection in a smartgrid or remote automation and control of health care systems, UEs mayhave low-latency, high-reliability transmission requirements, referredto herein as reliable ultra-low latency UEs (RULL-UEs). The latency andreliability requirements of RULL-UEs may be such that a successfultransmission is desired in a time period shorter than the time for an UEto receive ACK/NACK feedback in normal operation of a grant-free uplinktransmission scheme. In teleprotection in a smart grid, for example, therequirements for transmission may be less than 8 ms latency with 99.999%reliability. Thus, the desired low-latency and requirements of RULL-UEsmay not be attainable in a normal operation of a grant-free uplinktransmission scheme.

In order to provide improved the latency and reliability response in agrant-free uplink transmission scheme, the present disclosure provides areliable ultra-low latency (RULL) transmission mechanism in which aRULL-UE transmits a first transmission on one of the CTUs in a firsttransmission time interval (TTI), then the RULL-UE automaticallytransmits at least one redundant transmission, each redundanttransmission may be sent in a subsequent TTI on a different CTU than theinitial transmission. The first redundant transmission may be sent, forexample, in the TTI immediately after the TTI in which initialtransmission is sent. Utilizing a RULL mechanism, the latency betweentransmission and redundant transmissions may be, for example, 2 ms,compared to, for example, an 8 ms latency under normal operation of agrant-free uplink transmission scheme in which a random backoffprocedure is utilized, as described above.

Regrouping the CTUs that the RULL-UEs transmit on and automaticallysending redundant transmissions after an initial transmission increasesthe probably that one of the transmissions of each RULL-UE will bedecoded at the BS 102 without the RULL-UEs waiting for ACK/NACKfeedback, increasing the reliability and reducing the latency of theuplink transmission compared to the normal operation of the grant-freeuplink transmission scheme.

Referring now to FIG. 3A, a flow chart illustrating a method forimplementing a RULL transmission mechanism in a grant-free uplinktransmission scheme by a BS 102 is shown. The method may be carried outby software executed, for example, by a processor of the BS 102. Codingof software for carrying out such a method is within the scope of aperson of ordinary skill in the art given the present disclosure. Themethod may contain additional or fewer processes than shown and/ordescribed, and may be performed in a different order. Computer-readablecode executable by at least one processor of the BS 102 to perform themethod may be stored in a computer-readable medium, such as anon-transitory computer-readable medium. In some embodiments, theprocessor of the BS 102 that performs at least a portion of the methodmay be, for example, a remotely located controller in communication withthe BS 102. For example, in some embodiments a remotely locatedcontroller may implement the mapping scheme, while a processor locatedat the BS 102 may signal the mapping scheme, and other information, tothe UEs.

At 302, a BS 102 defines one or more reliable ultra-low latency CTU(RULL-CTU) access regions. Defining the RULL-CTU access region includesmapping, by the BS 102, various RULL-CTU to the RULL-CTU access regionutilizing a CTU mapping scheme. Mapping may include assigning a uniqueRULL-CTU index to each RULL-CTU in the RULL-CTU access region. EachRULL-CTU index corresponds to a RULL-CTU that a RULL-UE may performtransmissions on according to the RULL transmission mechanism.

In some embodiments, all initial transmissions and redundanttransmission by RULL-UEs are sent in the RULL-CTU access regions. Inother embodiments, some of the initial transmissions and redundanttransmission may be sent in a regular CTU access regions, while otherinitial transmissions and redundant transmissions are sent in theRULL-CTU access regions. In an example, described in more detail belowwith reference to FIG. 8, all initial transmissions by RULL-UEs are sentin a RULL-CTU access region, and all redundant transmissions are sent ina regular CTU access region.

At 304, the BS 102 identifies a portion of the UEs 104-118 within thecoverage area 120 as RULL-UEs. Identifying a UE as an RULL-UE mayutilize, for example, high-level signaling between the BS 102 and theUEs 104-118. The determination of a RULL-UE may be based on the servicesoperating on the RULL-UE such as, for example, a remote-healthapplication or a smart grid application. Identification may occur, forexample, when a UE 104-118 enters the coverage region 120 and connectionsetup signaling between the BS 102 and the UEs 104-118 is sent.Connection setup signaling may also occur when new services areavailable at a UE 104-118 within the coverage area 120 such as, forexample, by installation of new software having a low-latency highreliability transmission requirements.

The BS 102 may adjust the size of the RULL-CTU access region based onthe number of RULL-UE within the coverage area 120 determined throughconnection setup signaling. For example, if a large number of RULL-UEsare identified, the BS 102 may allocate a larger portion of theavailable bandwidth to the RULL-CTU access regions. Identifying at 304may include determining a number of redundant transmissions of theRULL-UEs. The number of redundant transmission may be based on thereliability mode. Identifying may also include applying a selectiveredundancy scheme. As described in more detail below, the reliabilitymode and the selective redundancy modes may determine how many and onwhich subsequent TTIs redundancy transmissions are sent.

At 306, the BS 102 may use high-level signaling, for example, through abroadcast channel, to send information to the RULL-UEs regarding theRULL-CTU indexing within the CTU access region to enable RULLtransmissions from RULL-UEs via the RULL transmission mechanism. Otherchannels such as, for example multicast or unicast channels, can beutilized as well. This high-level signaling may include, for example,information on the defined RULL-CTU access regions, number of RULL-CTUsin the access regions and/or RULL-CTU index map. The high-levelsignaling may also include assigned RULL-UE DCS index information, andthe like. The RULL-UEs determine which of the RULL-CTUs of the RULL-CTUaccess region to map to according to RULL mapping rules. Mapping rulesmay be defined in a default RULL mapping scheme. The default RULLmapping scheme may be determined by the BS 102 and sent to the RULL-UEsthrough high-level signaling, or may be determined by a standard.

The default RULL mapping scheme includes rules for mapping the RULL-UEsto the RULL-CTUs in an initial pattern for initial transmissions, andmapping the RULL-UEs to the RULL-CTUs in a regrouped pattern for each ofthe redundant transmissions. By utilizing a default mapping scheme, theinitial pattern and the regrouped pattern are implicitly known at the BS102. The mapping rules may be based on, for example, RULL-UEsidentification such as the RULL-UEs DCS or the RULL-UEs DCS indexassigned by a BS 102, the total number of RULL-CTUs, the time-frequencyresource ID, and/or other parameters such as subframe number.

At 308, the BS 102 receives the initial transmissions from the RULL-UEsin a first TTI and receives the redundant transmissions from theRULL-UEs in subsequent TTIs. In some embodiments, the RULL-UE maydetermine multiple RULL-CTUs for sending multiple redundanttransmissions on in respective multiple subsequent TTIs. The number ofredundant message sent by a RULL-UE may be determined by, for example, areliability transmission mode and/or a selective redundancy scheme ofthe RULL-UE.

At 310, the BS 102 attempts to resolve collisions that occur in eitherof the initial transmissions and the redundant transmissions.Transmitting initial and redundant transmissions increases thelikelihood that one of the transmissions will be decodable at the BS102. As discussed in more detail below, a decoded signal from one of thetransmissions may be utilized to resolve a collision that includes thedecoded signal during other transmissions. Resolving the collision mayinclude for example, subtracting the signal, decoded from othertransmissions, from the collision signal to resolve the transmissionfrom the other RULL-UE involved in the collision.

Referring now to FIG. 3B, a flow chart illustrating an alternativemethod for implementing a RULL transmission mechanism in a grant-freeuplink transmission scheme by a BS 102 is shown. The method may becarried out by software executed, for example, by a processor of the BS102. Coding of software for carrying out such a method is within thescope of a person of ordinary skill in the art given the presentdisclosure. The method may contain additional or fewer processes thanshown and/or described, and may be performed in a different order.Computer-readable code executable by at least one processor of the BS102 to perform the method may be stored in a computer-readable medium,such as a non-transitory computer-readable medium. In some embodiments,the processor of the BS 102 may be, for example, a remotely locatedcontroller in communication with the BS 102. For example, in someembodiments a remotely located controller may implement the mappingscheme, while a processor located at the BS 102 may signal the mappingscheme, and other information, to the UEs.

Steps 322-330 of the method of FIG. 3B are substantially similar tosteps 302-310 described above with reference to FIG. 3A and are notfurther described to avoid repetition.

At 332, a determination whether the number of collisions meets athreshold is made. The number of collisions may be, for example, thetotal number of collisions occurring during the initial and redundanttransmissions or may be the number of collisions occurring during theinitial transmissions only. The threshold may be set by the BS 102, thenetwork 100, or by a standard. The threshold may be, for example, thatcollisions occurs in less than 1% of the transmissions.

If the number of collisions does not meet the threshold, the methodreturns to step 328. If the number of collisions meets the threshold,the BS 102 uses the number of collisions and the overall conditions,such as for example the distribution of active RULL-UEs in theRULL-CTUs, to make decision on remapping the RULL-UEs to other RULL-CTUindexes in the same or a different CTU access region 324. The BS 102then returns to step 326 to send the remapped RULL-CTU information viahigh-level signaling (e.g., broadcast, multicast, or unicast) to theRULL-UEs in the coverage area 120.

Referring to FIG. 4, a flow chart illustrating RULL-UE activityaccording to various embodiments is shown. The method may be carried outby software executed, for example, by a processor of a RULL-UE. Codingof software for carrying out such a method is within the scope of aperson of ordinary skill in the art given the present disclosure. Themethod may contain additional or fewer processes than shown and/ordescribed, and may be performed in a different order. Computer-readablecode executable by at least one processor of the RUL-UE to perform themethod may be stored in a computer-readable medium, such as anon-transitory computer-readable medium.

At 402, a RULL-UE enters a BS's 102 coverage area 120. In step 404, theRULL-UE receives high-level signaling information from the BS 102. Thishigh level signaling information may include RULL-CTU access regiondefinitions, total number of RULL-CTUs, and the like. The high-levelsignaling at 402 may also include the default RULL mapping rules.Alternatively, the RULL-UE may be preconfigured with default RULLmapping rules.

At 406, the RULL-UE determines an appropriate first RULL-CTU to conductan initial transmission on in a first TTI, and an appropriate secondRULL-CTU to conduct a redundant transmission on in a second TTIsubsequent to the first TTI. The RULL-UE may determine the appropriatefirst and second RULL-CTU indexes using the default RULL mapping rules.

In some embodiments, the RULL-UE may determine multiple RULL-CTUs forsending multiple redundant transmissions on in respective multiplesubsequent TTIs. The number of redundant message sent may be determinedby, for example, a reliability transmission mode of the RULL-UE.

At 408, the RULL-UE sends the initial transmission on the first RULL-CTUin the first TTI, and sends the redundant transmission on the secondRULL-CTU in the second TTI. As discussed above, in some embodiments, theRULL-UE may send multiple redundant transmissions in respective multiplesubsequent TTIs. In some embodiments, the RULL-UE may send the redundanttransmission in a time pattern of TTIs, rather than the TTIs thatimmediately follow the TTI in which the initial transmission was made.Subsequent TTIs during which the RULL-UE sends a redundant transmissionmay be determined by, for example, a selective redundancy scheme, asdiscussed in more detail below.

Referring now to FIG. 5, an example illustrating default RULL mappingscheme in an RULL transmission mechanism in a grant-free uplinktransmission scheme is shown. In the example, a group of eight RULL-UEs,UE1 to UE8, are identified as reliable ultra-low latency UEs. TheRULL-UEs are mapped to four RULL-CTUs, 502-508 according to the defaultRULL mapping scheme that sets out the mapping rules for initialtransmission and redundant transmissions. In the example shown in FIG.5, the RULL-UEs are configured to transmit two redundant transmissions,in TTI2 and TTI3, after transmitting an initial transmission in TTI1.

In the example shown in FIG. 5, during TTI1 the RULL-UEs are mapped inan initial pattern in which UE1 and UE2 are mapped to RULL-CTU 502, UE3and UE4 are mapped to RULL-CTU 504, UE 5 and UE 6 are mapped to RULL-CTU506, and UE7 and UE8 are mapped to RULL-CTU 508. After the initialtransmission during TTI1, the RULL-UEs are regrouped for into a firstregrouped pattern in which UE1 and UE5 are mapped to RULL-CTU 502, UE2and UE6 are mapped to RULL-CTU 504, UE3 and UE7 are mapped to RULL-CTU306, and UE4 and UE8 are mapped to RULL-CTU 308. After the firstredundant transmission during TTI2, the RULL-UEs are regrouped into asecond regrouped pattern in which UE1 and UE3 are mapped to RULL-CTU502, UE5 and UE7 are mapped to RULL-CTU 504, UE2 and UE4 are mapped toRULL-CTU 306, and UE6 and UE8 are mapped to RULL-CTU 508.

In some embodiments, all RULL-UEs are included in the regrouped patternregardless of whether a particular RULL-UE has transmitted during TTI1or not. By regrouping all RULL-UEs, an even distribution of the RULL-UEsmay be maintained. RULL-UEs mapped to during subsequent TTIs after atransmission is inhibited. In other embodiments, only RULL-UEs areregrouped after an initial transmission. However, in these embodiments,transmitting RULL-UEs may be regrouped to CTUs in which non-transmittingRULL-UEs are mapped to, which may lead to an uneven and unpredictabledistribution of RULL-UEs.

For clarity, only one group of RULL-UEs, UE1 to UE8, is shown in FIG. 5.However, in some embodiments, a RULL transmission mechanism may includemore than one group of RULL-UEs such that RULL-UEs from the other groupsmay be mapped to RULL-CTUs 502-508, such that the mappings of the othergroups overlap with mappings of the group of RULL-UEs, UE1 to UE8, shownin FIG. 5. For example, at least some of the RULL-UEs of a second groupmay be mapped to the RULL-CTUs 502-508 shown in FIG. 5 for an initialtransmission in TTI2. In this example, at least some of the RULL-CTUsmapped to the second group of RULL-UEs for the initial transmissionsoverlap with the RULL-CTUs 502-508 mapped to the first group ofRULL-UEs, UE1 to UE8, for redundant transmissions.

Referring now to FIG. 6, an example illustrating how collisions may beresolved utilizing the RULL transmission mechanism is described. In thisexample, five RULL-UEs, UE1, UE2, UE3, UE5, and UE8, transmit an initialtransmission in TTI1. The mapping rules followed by the RULL-UEs in FIG.6 follow the same rules as the example shown in FIG. 5. However, forclarity only one redundant transmission is shown after the initialtransmission in the example shown in FIG. 6.

In the initial transmission during TTI1, the signal received on RULL-CTU602 cannot be decodable by the BS, indicated by the starburst, due tothe collision of the transmissions of UE1 and UE2. Although the BS 102cannot decode the transmission on RULL-CTU 602 during TTI1, the BS 102may implicitly know that the collision results from transmissions fromUE1 and UE2 because the default RULL mapping rules set out that theseare the two RULL-UEs mapped to RULL-CTU 602 during TTI1. The initialtransmissions from UE3, UE5, and UE8 do not collide with othertransmissions and are decoded by the BS 102.

After the initial transmissions at TTI1, the RULL-UEs are regrouped intoa regrouped pattern and a redundant transmission is sent by all of theRULL-UEs. During TTI2, the redundant transmission from UE2 on RULL-CTU604 does not collide and is decoded by the BS 102. The redundanttransmissions from UE1 and UE5, received on RULL-CTU 602, collide inTTI2, as indicated by the starburst. Thus, the transmission from UE1cannot be decoded directly based on either of the initial transmissionor the redundant transmission.

However, the BS 102 may implicitly determine that the signal detected onRULL-CTU 602 in TTI2 is the combination of transmission from UE1 and UE5because the default RULL mapping scheme sets out that these are the twoRULL-UEs having redundant transmissions on RULL-CTU 602 at TTI2.

Thus, because the BS 102 has determined implicitly that collided signalsare a combination of UE1 and UE2 in TTI1 and UE1 and UE5 in TTI2, andbecause the transmission of UE5 was decoded in TTI1 and the transmissionfrom UE2 was decoded in TTI2, the transmission from UE1 may berecovered. For example, UE1's transmission may be recovered from thesignal received on RULL-CTU 602 in TTI2 by subtracting the transmissionfrom UE5 that was received on RULL-CTU 606 during TTI1. Alternatively,UE1's transmission may be recovered from the signal received on RULL-CTU602 in TTI1 by subtracting the transmission from UE2, received onRULL-CTU 604 during TTI2.

In some embodiments, the joint detection and decoding of initial andredundant transmissions, such as illustrated in the examples shown inFIGS. 6 and 7, is performed by an MPA receiver.

The number of regrouping and redundant transmissions that are sent by aRULL-UE may be determined based on the latency and reliabilityrequirements of the RULL-UE. For example, the RULL transmissionmechanism may include a number of reliability transmission modes toenable different RULL traffic types having different latency andreliability requirements. Reliability transmission modes are defined byphysical layer transmission parameters, such as, for example, the numberof redundant transmissions that are sent, and any selective redundancyscheme utilized, which are described in more detail below.

As an example, teleprotection in a smart grid has a longer latency andhigher reliability requirement, for example 8 ms latency and 99.999×reliability, than remote automation and control transmission, which hasa shorter latency and lower reliability requirement, for example 2-3 mslatency and 99.9% reliability. Thus, teleprotection in a smart grid mayutilize different reliability transmission modes than remote automationand control transmission. For example, teleprotection in a smart gridmay utilize a reliability transmission mode having a greater number ofredundant transmissions, for example 4-8 redundant transmissions, thanthe reliability transmission mode utilized by remote automation andcontrol, which transmit, for example, 2-3 redundant transmissions.

In addition to the number of redundancy transmissions sent by theRULL-UEs, in some embodiments the RULL-UEs may be configured to transmitredundant transmissions in a particular pattern of TTIs following theinitial transmission, rather than in the TTIs immediately following aninitial transmission. Which TTIs a RULL-UE will transmit redundanttransmissions may be defined in a selective redundancy transmissionscheme. The selective redundancy transmission scheme may be one of, forexample, an UE selectively redundancy transition scheme, a CTU selectiveredundancy transmission scheme, or a time selective redundancytransmission scheme.

In an UE selective redundancy transmission scheme, one portion of theRULL-UEs send redundant transmissions in a particular TTI, while theremaining portion does not. Whether or not RULL-UEs send redundanttransmissions may be defined implicitly by rules based on, for example,the RULL-UE DCS and TTI number. For example, the UE selective redundancytransmission scheme may be such that RULL-UEs having an even-numberedDSC will transmit a redundant transmission only during even-numberedTTIs following the initial transmission.

In a CTU selective redundancy scheme, the determination of whichRULL-UEs will transmit a redundant transmission during a particular TTIis based on the RULL-CTUs that the UEs are transmitting on. The CTUselective redundancy scheme may be based on, for example, the RULL-CTUindexes. For example, all RULL-UEs mapped to a RULL-CTU having aneven-numbered RULL-CTU index will transmit redundant transmissions whileall RULL-UEs mapped to an odd-numbered RULL-CTU index will not transmitredundancy transmissions.

In a time selective redundancy scheme, the RULL-UEs are configured totransmit redundant transmissions according to a predetermined TTIpattern such as, for example, every TTI, or every other TTI, followingan initial transmission. The time selective redundancy scheme may beutilized together with either the UE selective redundancy transmissionscheme or the CTU selective redundancy transmission scheme. For example,when the time selective and UE selective redundancy schemes are utilizedtogether, the predetermined TTI pattern of the time selective redundancyscheme may be applied to a particular RULL-UE determined under the UEselective redundancy scheme. In another example, when the time selectiveand CTU selective redundancy schemes are utilized together, thepredetermined TTI pattern of the time selective redundancy scheme may beapplied to a RULL-UEs mapped to a particular CTU as determined under theCTU selective redundancy scheme.

The selective redundancy transmission scheme utilized may be based onthe latency and reliability requirements. For example, RULL-UEs withlower latency and higher reliability requirements may be configured toutilize selective redundancy transmission schemes with a greater numberof redundant transmissions over a period of fewer TTIs than RULL-UEshaving higher latency and lower reliability requirements.

Referring to FIG. 7, examples of implementing selective redundancytransmission schemes are described.

Similar to the example shown in FIG. 5, five RULL-UEs, UE1, UE2, UE3,UE5, and UE8, are transmitting data utilizing the RULL transmissionscheme. The RULL-UEs are mapped into initial patterns and regroupedpatterns similar to those of the examples shown in FIGS. 5 and 6.However, in the example shown in FIG. 7, only UE1, UE3, and UE5 transmitredundant transmissions during TTI2 according to a selective redundancytransmission scheme.

In an embodiment, the selective redundancy transmission scheme utilizedin the example shown in FIG. 7 is a UE selective redundancy scheme inwhich the RULL-UEs having, for example, an odd-numbered RULL-UE ID,i.e., UE1, UE3, and UE5, transmit a redundancy transmission in TTI2,while the RULL-UEs even-numbered UE ID, i.e., UE2 and UE8, do nottransmit a redundancy transmission in TTI2.

In another embodiment, the selective redundancy transmission schemeutilized in the example shown in FIG. 7 is a CTU selective redundancytransmission scheme in which the RULL-UEs mapped to RULL-CTUs 702 and706 in TTI2 transmit redundant transmissions, and RULL-UEs mapped toRULL-CTUs 704 and 708 in TTI2 do not transmit redundant transmissions.Thus, UE1 and UE5, mapped to CTU 702, and UE3, mapped to CTU 706,transmit redundant transmissions in TTI2. UE2, mapped to CTU 704, andUE8, mapped to CTU 708, do not transmit redundant transmissions.

To recover the collided transmissions at RULL-CTU 702 in TTI1 and TTI2in the example shown in FIG. 7, the transmission from UE1 is recoveredby subtracting the transmission from UE5 decoded from CTU 706 in TTI1from the collided transmission received at RULL-CTU 702 in TTI2. Therecovered transmission from UE1 may then be utilized to recover thetransmission from UE2 by subtracting the UE1 transmission from thecollided transmission received on CTU 702 in TTI1.

Referring now to FIG. 8, in some embodiments, implementing the RULLtransmission mechanism may include dedicating a RULL-CTU access region802 to initial transmissions of the RULL transmission mechanism, andutilizing a regular CTU access region 804 for redundant transmissionsfrom RULL-UEs.

Utilizing a RULL-CTU access region 802 dedicated for initialtransmissions avoids mixing initial transmissions and redundanttransmissions within the same RULL-CTU region, which increases thecomplexity in keeping track of transmissions. When a collision occurs ina RULL-CTU of the RULL-CTU access region 802, the BS 102 knows that thetransmission involved in the collision are initial transmissions and candetermine which RULL-UEs were potentially involved utilize the defaultRULL-mapping rules, without having to determine if any RULL-CTUs aremapped to that same CTU for redundant transmissions. Further, knowingthat a collision involves initial transmissions enables the BS 102 toanticipate the CTUs of the regular CTU access region 804 that redundanttransmissions are expected on in subsequent TTIs.

In the example shown in FIG. 8, two RULL-UEs, represented by the blackcircle 806 and the white circle 808, are mapped to a RULL-CTU 810 in theRULL-CTU access region 802. At TTI1, both RULL-UEs 806 and 808 transmitan initial transmission on RULL-CTU 810, resulting in a collision atRULL-CTU 810, indicated by the starburst.

Based on the default mapping scheme, the BS 102 may implicitly determinethat the potential RULL-UEs of the transmission, i.e., the RULL-UEsmapped to RULL-CTU 810 for an initial transmission, include RULL-UEs 806and 808. Based on the implicit knowledge, the BS 102 can anticipate thatpotential redundancy transmissions in TTI2 will be received on CTU 812and CTU 814, and in TTI3 on CTU 816 and CTU 818.

Further, having an RULL-CTU access region 802 dedicated for initialtransmissions makes resolving collisions easier at the BS 102 byavoiding the BS 102 having to consider a redundant transmission from oneRULL-UE colliding with an initial transmission from another RULL-UE. Ina grant-free uplink transmission scheme having high levels of RULLtraffic, determining which transmissions are initial transmissions andwhich are redundant transmissions can be computationally intensive. Bydefining a RULL-CTU access region 802 dedicated to initialtransmissions, the BS 102 can easily determine that any transmissionsreceived in the RULL-CTU access region 802 are initial transmissions.

Within the regular CTU access region 804, the BS 102 may distinguish theRULL grant-free uplink transmission traffic from the regular grant-freeuplink transmission traffic implicitly, utilizing the default mappingrules, or explicitly, based on headers of the received transmissions.

FIG. 9 is a block diagram of a processing system that may be used forimplementing the devices and methods disclosed herein. Specific devicesmay utilize all of the components shown, or only a subset of thecomponents and levels of integration may vary from device to device.Furthermore, a device may contain multiple instances of a component,such as multiple processors, memories, transmitters, receivers, etc. Theprocessing system may comprise a processor operationally coupled to oneor more input/output devices, such as a speaker, microphone, mouse,touchscreen, keypad, keyboard, printer, display, and the like. Theprocessing unit may include a processor, memory, display controller, andan input/output interface connected to a bus.

The bus may be one or more of any type of several bus architecturesincluding a memory bus or memory controller, a peripheral bus, videobus, or the like. The processor may comprise any type of electronic dataprocessor. The memory may comprise any type of system memory such asstatic random access memory (SRAM), dynamic random access memory (DRAM),synchronous DRAM (SDRAM), read-only memory (ROM), a combination thereof,or the like. In an embodiment, the memory may include ROM for use atboot-up, and DRAM for program and data storage for use while executingprograms. The memory may also include a storage device configured tostore data, programs, and other information and to make the data,programs, and other information accessible via the bus. The storagedevice may comprise, for example, one or more of a solid state drive,hard disk drive, a magnetic disk drive, an optical disk drive, or thelike.

The display controller and the input/output interface provide interfacesto couple external input and output devices to the processing unit.Examples of input and output devices include a display coupled to thedisplay controller, and a mouse, keyboard, or printer coupled to theinput/output. Other devices may be coupled to the processing unit, andadditional or fewer interface cards may be utilized.

The processing unit also includes one or more network interfaces, whichmay comprise wired links, such as an Ethernet cable, and/or wirelesslinks to access nodes or different networks. The network interfaceallows the processing unit to communicate with remote units via thenetwork. For example, the network interface may provide wirelesscommunication via one or more transmitters/transmit antennas and one ormore receivers/receive antennas. In an embodiment, the processing unitis coupled to a local-area network or a wide-area network for dataprocessing and communications with remote devices, such as otherprocessing units, the Internet, remote storage facilities, or the like.

In an example 1, there is provided a method comprising: implementing, bya base station (BS), a reliable ultra-low latency (RULL) transmissionmechanism in a grant-free uplink transmission scheme, the grant-freeuplink transmission scheme having defined therein contentiontransmission unit (CTU) access regions and a plurality of CTUs; whereinimplementing the reliable ultra-low latency transmission mechanismcomprises: defining a reliable ultra-low latency user equipment(RULL-UE) mapping scheme by mapping a plurality of RULL-UEs to theplurality of CTUs in an initial pattern for initial transmissions in afirst transmission time interval (TTI), and mapping the plurality ofRULL-UEs to the plurality of CTUs in a regrouped pattern for redundanttransmissions in a second TTI subsequent to the first TTI, wherein theinitial pattern is different from the regrouped pattern.

In an example 2, there is provided a method according to example 1,wherein implementing the RULL transmission mechanism comprises: defininga reliable ultra-low latency CTU (RULL-CTU) access region from a portionof the CTU access regions of the grant-free transmission scheme; anddefining an RULL-CTU mapping scheme by mapping at least a portion of theplurality of CTUs to the RULL-CTU access region to define a plurality ofRULL-CTUs.

In an example 3, there is provided a method according to example 2,wherein defining the RULL-UE mapping scheme includes mapping theplurality of the RULL-UEs to the plurality of RULL-CTUs in the initialpattern and the regrouped pattern.

In an example 4, there is provided a method according to example 2,wherein defining the RULL-UE mapping scheme includes mapping theplurality of the RULL-UEs to the plurality of RULL-CTUs in the initialpattern and mapping the plurality of RULL-UEs to the plurality of CTUsin the regrouped pattern.

In an example 5, there is provided a method according to example 1,wherein implementing the RULL transmission mechanism further comprises:receiving, by the BS, the initial transmissions in the first TTI and theredundant transmissions in the second TTI, wherein the BS does nottransmit acknowledge or negative acknowledgement (ACK/NACK) feedbackbetween receiving the initial and redundant transmissions; resolvingcollisions utilizing the initial transmissions, the redundanttransmissions, and the mapping scheme.

In an example 6, there is provided a method according to example 5,wherein implementing the RULL transmission mechanism further comprises:defining a remapping scheme by mapping a plurality of RULL-UEs to theplurality of CTUs in a second initial pattern for initial transmissionsin the first TTI, and a second regrouped pattern for redundanttransmissions in the second TTI subsequent to the first TTI when the BSdetermines the number of collisions in at least one of the initialtransmissions and redundant transmissions meets a threshold, wherein thesecond initial pattern is different than the first initial pattern, andthe second regrouped pattern is different than the first regroupedpattern and the second initial pattern; and sending information relatedto the remapping scheme to the RULL-UEs using high-level signaling.

In an example 7, there is provided a method according to example 5,wherein the initial transmissions and the redundant transmissions arebased on a sparse code multiple access (SCMA) scheme.

In an example 8, there is provided a method according to example 7,further comprising joint detecting and decoding of the initialtransmission and the redundant transmission utilizing a message parsingalgorithm (MPA).

In an example 9, there is provided a method according to example 1,wherein implementing the RULL transmission mechanism further comprisesdefining a first portion of the plurality of RULL-UEs that transmitredundant transmissions in the second TTI, and a remaining portion ofthe plurality of RULL-UEs do not transmit redundant transmissions in thesecond TTI.

In an example 10, there is provided a method according to example 9,wherein the first portion of the plurality of RULL-UEs is defined basedon RULL-UE identifications of the plurality of RULL-UEs.

In an example 11, there is provided a method according to example 9,wherein the first portion of the plurality of RULL-UEs is defined basedon the CTUs that the first portion is mapped to in the regroupedpattern.

In an example 12, there is provided a method according to example 9,wherein the first portion of the plurality of RULL-UEs is defined basedon the TTI that the redundant transmission is transmitted in.

In an example 13, there is provided a method according to example 1,wherein defining the RULL-UE mapping scheme includes mapping theplurality of RULL-UEs to the CTUs in a plurality of unique regroupedpatterns, each unique regrouped pattern for a respective one of aplurality of redundant transmissions, each redundant transmission in arespective one of a plurality of TTIs subsequent to the first TTI.

In an example 14, there is provided a method according to example 13,wherein the number of the plurality of redundant transmissions isdetermined based on one or both of a latency requirement and areliability requirement of the plurality of RULL-UEs.

In an example 15, there is provided a method according to example 1,wherein the plurality of CTUs are frequency resources.

In an example 16, there is provided a method according to example 1,wherein the plurality of CTUs are time resources.

In an example 17, there is provided a method according to example 1,wherein defining a RULL-UE mapping scheme comprises mapping a secondplurality of

RULL-UEs to the plurality of CTUs in a second initial pattern forinitial transmissions in second TTI, and mapping the second plurality ofRULL-UEs to the plurality of CTUs a second regrouped pattern forredundant transmissions in a third TTI subsequent to the second TTI, theCTUs mapped to the second plurality of RULL-UEs in the second initialpattern at least partially overlaps the CTUs mapped to the firstplurality of RULL-UEs in the regrouped pattern.

In an example 18, there is provided a base station (BS) comprising: ahardware processor; and a computer readable storage medium having storedthereon computer readable code for execution by the processor to:implement a reliable ultra-low latency (RULL) transmission mechanism ina grant-free uplink transmission scheme, the grant-free uplinktransmission scheme having defined therein contention transmission unit(CTU) access regions and a plurality of CTUs, wherein implementing theRULL transmission mechanism comprises: defining a reliable ultra-lowlatency user equipment (RULL-UE) mapping scheme by mapping a pluralityof RULL-UEs to the plurality of CTUs in an initial pattern for initialtransmissions in a first transmission time interval (TTI), and mappingthe plurality of RULL-UEs to the plurality of CTUs in a regroupedpattern for redundant transmissions in a second TTI subsequent to thefirst TTI, wherein the initial pattern is different from the regroupedpattern.

In an example 19, there is provided a BS according to example 18,wherein implementing the RULL transmission mechanism further comprises:defining a reliable ultra-low latency CTU (RULL-CTU) access region froma portion of the CTU access regions of the grant-free transmissionscheme; and defining an RULL-CTU mapping scheme by mapping at least aportion of the plurality of CTUs to the RULL-CTU access region to definea plurality of RULL-CTUs.

In an example 20, there is provided a BS according to example 19,wherein defining the RULL-UE mapping scheme includes mapping theplurality of the RULL-UEs to the plurality of RULL-CTUs in the initialpattern and the regrouped pattern.

In an example 21, there is provided a BS according to example 19,wherein defining the RULL-UE mapping scheme includes mapping theplurality of the RULL-UEs to the plurality of RULL-CTUS in the initialpattern and mapping the plurality of RULL-UEs to the plurality of CTUsin the regrouped pattern.

In an example 22, there is provided a BS according to example 18,wherein implementing the RULL transmission mechanism further comprises:receiving, by the BS, the initial transmissions in the first TTI and theredundant transmissions in the second TTI; resolving collisionsutilizing the initial transmissions, the redundant transmissions, andthe mapping scheme.

In an example 23, there is provided a BS according to example 18,wherein implementing the RULL transmission mechanism further comprisesdefining a first portion of the plurality of RULL-UEs that transmitredundant transmissions in the second TTI, and a remaining portion ofthe plurality of RULL-UEs do not transmit redundant transmissions in thesecond TTI.

In an example 24, there is provided a BS according to example 18,wherein defining the RULL-UE mapping scheme includes mapping theplurality of RULL-UEs to the CTUs in a plurality of unique regroupedpatterns, each unique regrouped pattern for a respective one of aplurality of redundant transmissions, each redundant transmission in arespective one of a plurality of TTIs subsequent to the first TTI.

In an example 25, there is provided a method comprising: implementing,by a reliable ultra-low latency user equipment (RULL-UE), a reliableultra-low latency (RULL) mechanism in a default reliable ultra-lowlatency contention transmission unit (RULL-CTU) mapping scheme by:determining a first contention transmission unit (CTU) for an initialtransmission in a first transmission time interval (TTI) in accordancewith an initial RULL-UE mapping rule and the default RULL-CTU mappingscheme; transmitting, to a base station (BS), the initial transmissionon the first CTU during the first TTI; determining a second CTU for aredundant transmission in a second TTI subsequent to the first TTI inaccordance with a redundant RULL-UE mapping rule and the defaultRULL-CTU mapping scheme; transmitting, to the BS, the redundanttransmission on the second CTU during the second TTI without receiving,at the RULL-UE, acknowledgement/negative acknowledgement (ACK/NACK)feedback from the BS.

In an example 26, there is provided a method according to example 25,wherein determining a second CTU includes determining a plurality ofredundant CTUs, each of the redundant CTUs for one of a plurality ofredundant transmissions, each redundant transmission in one of aplurality of TTIs subsequent to the first TTI; and wherein transmittingthe redundant transmission on the second CTU includes transmitting eachof the redundant transmissions on a respective one of the plurality ofCTUs during a respective one of the plurality of TTIs.

In an example 27, there is provided a method according to example 26,wherein transmitting the redundant transmission on the second CTUcomprises automatically transmitting a first portion of the plurality ofredundant transmissions, and not transmitting a remaining portion of theredundant transmissions.

In an example 28, there is provided a method according to example 27,wherein the first portion is determined based on the respective CTU thateach of the plurality of redundant transmissions transmits on.

In an example 29, there is provided a method according to example 27,wherein the first portion is determined based on the respective TTI thateach of the plurality of redundant transmissions transmit during.

In an example 30, there is provided a method according to example 25,wherein: the first CTU determined by the RULL-UE for the initialtransmission in the first TTI is mapped to a first CTU access region;and the second CTU determined by the RULL-UE for the redundanttransmission in the second TTI is mapped to a second CTU access regiondifferent from the first CTU access region.

In an example 31, there is provided a reliable ultra-low latency userequipment (RULL-UE) comprising: a hardware processor; and a computerreadable storage medium having stored thereon computer readable code forexecution by the processor to: implement a reliable ultra-low latency(RULL) transmission mechanism in a default reliable ultra-low latencycontention transmission unit (RULL-CTU) mapping scheme, whereinimplementing the RULL transmission mechanism comprises: determining afirst contention transmission unit (CTU) for an initial transmission ina first transmission time interval (TTI) in accordance with an initialRULL-UE mapping rule and the default RULL-CTU mapping scheme;transmitting, to a base station (BS), the initial transmission on thefirst CTU during the first TTI; determining a second CTU for a redundanttransmission in a second TTI subsequent to the first TTI in accordancewith a redundant RULL-UE mapping rule and the default RULL-CTU mappingscheme; transmitting, to the BS, the redundant transmission on thesecond CTU during the second TTI without receiving, at the RULL-UE,acknowledgement/negative acknowledgement (ACK/NACK) feedback from theBS.

In an example 32, there is provided a RULL-UE according to example 31,wherein determining a second CTU includes determining a plurality ofredundant CTUs, each of the redundant CTUs for one of a plurality ofredundant transmissions, each redundant transmission in one of aplurality of TTIs subsequent to the first TTI; and wherein transmittingthe redundant transmission on the second CTU includes automaticallytransmitting each of the redundant transmissions on a respective one ofthe plurality of CTUs during a respective one of the plurality of TTIs.

In an example 33, there is provided a RULL-UE according to example 32,wherein transmitting the redundant transmission on the second CTUcomprises automatically transmitting a first portion of the plurality ofredundant transmissions, and not transmitting a remaining portion of theredundant transmissions.

In an example 34, there is provided a RULL-UE according to example 33,wherein the first portion is determined based on the respective CTU thateach of the plurality of redundant transmissions transmits on.

In an example 35, there is provided a RULL-UE according to example 33,wherein the first portion is determined based on the respective TTI thateach of the plurality of redundant transmissions transmit during.

In an example 36, there is provided a RULL-UE according to example 31,wherein: the first CTU determined by the RULL-UE for the initialtransmission in the first TTI is mapped to a first CTU access region;and the second CTU determined by the RULL-UE for the redundanttransmission in the second TTI is mapped to a second CTU access regiondifferent from the first CTU access region.

In the preceding description, for purposes of explanation, numerousdetails are set forth in order to provide a thorough understanding ofthe embodiments. However, it will be apparent to one skilled in the artthat these specific details are not required. In other instances,well-known electrical structures and circuits are shown in block diagramform in order not to obscure the understanding. For example, specificdetails are not provided as to whether the embodiments described hereinare implemented as a software routine, hardware circuit, firmware, or acombination thereof.

Embodiments of the disclosure can be represented as a computer programproduct stored in a machine-readable medium (also referred to as acomputer-readable medium, a processor-readable medium, or a computerusable medium having a computer-readable program code embodied therein).The machine-readable medium can be any suitable tangible, non-transitorymedium, including magnetic, optical, or electrical storage mediumincluding a diskette, compact disk read only memory (CD-ROM), memorydevice (volatile or non-volatile), or similar storage mechanism. Themachine-readable medium can contain various sets of instructions, codesequences, configuration information, or other data, which, whenexecuted, cause a processor to perform steps in a method according to anembodiment of the disclosure. Those of ordinary skill in the art willappreciate that other instructions and operations necessary to implementthe described implementations can also be stored on the machine-readablemedium. The instructions stored on the machine-readable medium can beexecuted by a processor or other suitable processing device, and caninterface with circuitry to perform the described tasks.

The above-described embodiments are intended to be examples only.Alterations, modifications and variations can be effected to theparticular embodiments by those of skill in the art. The scope of theclaims should not be limited by the particular embodiments set forthherein, but should be construed in a manner consistent with thespecification as a whole.

1. A method comprising: configuring a first user equipment (UE), usingfirst high-level signaling, to perform a configured set of uplinkgrant-free transmissions including an initial uplink grant-freetransmission and at least one uplink grant-free redundant transmission,using time-frequency regions indicated by a first mapping, the firstmapping defining first time-frequency regions for the configured set ofuplink grant-free transmissions; and performing the configured uplinkgrant-free transmission(s), using the time-frequency regions by thefirst mapping, until an acknowledge (ACK) is received by the first UE.2. The method of claim 1, wherein each time-frequency region defined bythe first mapping and the second mapping is a contention transmissionunit (CTU) access region.
 3. The method of claim 2, wherein each CTUaccess region includes at least one of a pilot or a signature.
 4. Themethod of claim 1, wherein the grant-free transmission is successfulwhen the ACK is received.
 5. The method of claim 1, wherein thegrant-free is correctly decoded by a base station (BS) when the ACK isreceived.
 6. The method of claim 1, wherein the ACK is expected to bereceived by the first UE within a pre-configured time period.
 7. Themethod of claim 6, wherein the grant-free transmission fails when thefirst UE does not receive the ACK within the pre-configured time period.8. The method of claim 6, wherein the grant-free transmission is notcorrectly decoded by BS when the first UE does not receive the ACKwithin the pre-configured time period.
 9. The method of claim 1, whereinthe first high-level signaling is one of the following: unicast,multicast or broadcast signaling.
 10. An apparatus comprising: aprocessor; and a non-transitory computer-readable memory storing thereoninstructions that, when executed, cause the processor to: configure afirst user equipment (UE), using first high-level signaling, to performa configured set of uplink grant-free transmissions including an initialuplink grant-free transmission and at least one uplink grant-freeredundant transmission, using time-frequency regions indicated by afirst mapping, the first mapping defining first time-frequency regionsfor the configured set of uplink grant-free transmissions; and performthe configured uplink grant-free transmission(s), using thetime-frequency regions by the first mapping, until an acknowledge (ACK)is received by the first UE.
 11. The apparatus of claim 10 wherein eachtime-frequency region defined by the first mapping and the secondmapping is a contention transmission unit (CTU) access region.
 12. Theapparatus of claim 11, wherein each CTU access region includes at leastone of a pilot or a signature.
 13. The apparatus of claim 10, whereinthe grant-free transmission is successful when the ACK is received. 14.The apparatus of claim 10, wherein the grant-free is correctly decodedby a base station (BS) when the ACK is received.
 15. The apparatus ofclaim 10, wherein the ACK is expected to be received by the first UEwithin a pre-configured time period.
 16. The apparatus of claim 15,wherein the grant-free transmission fails when the first UE does notreceive the ACK within the pre-configured time period.
 17. The apparatusof claim 15, wherein the grant-free transmission is not correctlydecoded by BS when the first UE does not receive the ACK within thepre-configured time period.
 18. The apparatus of claim 10, wherein thefirst high-level signaling is one of the following: unicast, multicastor broadcast signaling.
 19. A non-transitory computer readable mediumhaving instructions encoded thereon, wherein the instructions whenexecuted by a processor of an apparatus, cause the apparatus to:configure a first user equipment (UE), using first high-level signaling,to perform a configured set of uplink grant-free transmissions includingan initial uplink grant-free transmission and at least one uplinkgrant-free redundant transmission, using time-frequency regionsindicated by a first mapping, the first mapping defining firsttime-frequency regions for the configured set of uplink grant-freetransmissions; and perform the configured uplink grant-freetransmission(s), using the time-frequency regions by the first mapping,until an acknowledge (ACK) is received by the first UE.
 20. Thenon-transitory computer readable medium of claim 19, wherein eachtime-frequency region defined by the first mapping and the secondmapping is a contention transmission unit (CTU) access region.